ICSdroid is lacking a setting that prevents to sync without wifi. It’d be pretty useful, not just to prevent using mobil data transmission, but also to prevent sync failures, which are possible when not having good mobile connection. Notice DAVdroid does offer the setting.
I’m using ICSx⁵ 1.9-standard and DAVx⁵ 3.3.8-ose (thanks), both from F-Droid. In DAVx⁵ I am subscribed to 1 caldav (Personal) and no webcal. In ICSx⁵ I am subscribed to 3 webcal - these are all public holidays and only change about once a year.
So in ICSx⁵ I’ve set the sync interval to manual, this in confirmed by a message shown on the bottom “Automatic sync disabled”. The problem is whenever a network connection is available ICSx⁵ still tries to sync even when it’s not supposed to.